1. Field of the Invention
The invention disclosed and claimed herein generally pertains to an apparatus and method for monitoring or inspecting molded foam parts. More particularly, the invention pertains to apparatus of the above type wherein the molded foam parts are formed by fusion of plastic beads. Even more particularly, the invention pertains to apparatus of the above type that enables inspection of molded foam part fusion to be improved, substantially simplified, and does not cause damage to the parts.
2. Description of the Related Art
Molded foam parts are used extensively, for package cushioning as well as for other important applications. For example, computer equipment and other electronic products typically must be protected against impact or rough handling, and may be of irregular shape. Accordingly, molded foam is commonly used to secure the product firmly within a shipping carton. The molded foam cushions also serve to protect the product from sudden shock, impacts or the like.
The manufacture of cushions or other parts from molded foam is comparatively inexpensive, and parts can be formed into virtually any shape desired. Molded foam parts are made by the fusion of plastic beads, where the beads are made from plastic material such as expandable polystyrene, polypropylene or polyethylene. The fusion occurs when plastic beads are placed inside a mold or other tooling, and subjected to steam heat and pressure to make them expand and fuse together. The beads are thus fused to form a part, wherein part shape is determined by the mold.
The strength and durability of molded foam parts is very important for many applications, particularly if the parts are to be used to cushion comparatively fragile parts or products as described above. Strength and cushioning characteristics of a molded foam part are largely determined by the quality of the bead fusion. This quality, in turn, is determined by the degree of fusion, that is, the extent to which the beads have bonded during the molding process. Clearly, for many applications it will be essential to know whether the bead fusion quality in a part is or is not at an acceptable level.
Currently, there are no known reliable and repeatable techniques available to measure bead fusion. Most current methods used to determine bead fusion are manual systems that require the destruction of the part being tested. For example, an inspector must break apart or cut the part being inspected, in order to visually inspect the bead fusion quality. More particularly, the inspector must view the expanded beads, to see if they remain intact or are torn apart, a torn bead being a sign of good fusion. By counting the ratio of intact beads to torn beads, a rough indication of fusion quality is provided. However, the beads are very small and it is frequently difficult to tell whether they are torn or not. Thus, this process tends to be unreliable, as well as being tedious, time-consuming and destructive to the tested part.
A further inspection method involves taking a cross-section of the part, and then increasing stress on the part until it cracks. Again, this method is destructive to the part but is still unreliable. The selection of the cross-section can cause stress lines in the material that affect the test, without necessarily indicating the over-all bead fusion quality. In a third method, a probe is placed on the surface of a molded foam part, to measure resistance. This method, while comparatively quick and non-destructive to the part, has proven to be unreliable. A skin that forms on the external wall of the part can prevent detection of fusion deficiencies that are deep within the part.
It is thus apparent that a new device or method is needed to test fusion quality in molded foam parts, wherein test results are accurate and reliable, and the tested parts are not destroyed or damaged. In addition, users of the device should require only a low level of training or skill.